1. Field of the Invention
The present invention relates to a method and apparatus for adjusting chroma and, in particular, to such method and apparatus which can be applied when white balance is automatically adjusted by an internal light measurement system.
2. Description of the Related Art
Conventionally, an automatic white balance adjusting method includes an external light measurement system and an internal light measurement system. In the external light measurement system, color temperatures are measured by an external sensor and the control signal that is obtained from such measurement is used to control the gains of red and blue signals.
On the other hand, the internal light measurement system is a control system which is based on a general fact that averaging of colors on the entire screen provides a grey color. That is, even when a general object is photographed, if the colors are averaged over the entire screen, then there is provided a color which is equivalent to that obtained when a white object is photographed.
In other words, the internal light measurement system is a control system based on a premise that colors in a screen are often distributed equally on the positive and negative sides of axes, (R - Y) and (B - Y). In this control system, color signals (E.sub.R - E.sub.Y) and (E.sub.B - E.sub.Y) are respectively integrated over the entire screen and the gains of red and blue signals are adjusted or controlled so that the resultant integration average value can coincide with a reference level showing a predetermined grey color.
In the above-mentioned automatic white balance adjusting method using the external light measurement system, colors can be reproduced comparatively well even when chroma is low, for instance, when a scene is in the shade, under dark illumination or the like. However, in the automatic white balance adjusting method using the internal light measurement system, it is difficult to reproduce colors well when chroma is low, which is a contemplated problem to be solved.